Cloud points of aqueous solutions of homogeneous poly(oxyethylene)dodecyl ether derivatives (C12(OE)n : 1"/= 2-8) and the apparent theta temperature TO ap were determined from the abrupt changes in optical transmittance and the temperature dependence of the second viriai coefficient obtained by light scattering measurements. It was found that the lower critical solution temperature (LCST) shifts to a lower temperature and lower concentration as the number of oxyethylene units in a molecule decreases. Because of this behavior of LCST, the modified Flory-Schultz plot of phase separation was applied to the present nonionie surfactant-water system, and its theta temperature obtained. The dependence of TO ap on the number of oxyethylene units suggests that the polyoxyethylene chain has different effects on the solubility of C12(OE)n in water for n less than or equal to 3 from those for n greater than or equal to 4.

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Poly-l-butene gels in some solvents of benzene-derivatives show a colouring phenomenon. The colour changes from blue to yellow under irradiation of natural light as the temperature rises from the melting point of the solvent to the sol-gel transition temperature. The colouring phenomenon is due to selective scattering, but not to optical absorption. The apparent characteristics of the phenomenon resemble the thermochromism of cholesteric liquid crystals, although poly-l-butene itself is colourless and has no asymmetric carbons.

ABSTRACT:Sol-gel transitions of a series of fractionated low-density polyethylenes in cyclohexane--{:arbondisulfide were studied. Gelation temperatures increased with polymer concentration as well as molecular weight. Experimental data were analyzed by a theory proposed by Takahashi, Sakai and Kato for the gel-melting temperature of branched polymers. This theory was found to apply well to the experimental data. The results of our study suggest that the size of the crystalline junction is independent of the molecular weight of fractionated samples.KEY WORDS Sol-Gel Transition I Gel I Gel-Melting Temperature Polyethylene I Branched Polyethylene I Low Density Polyethylene I It is well known that polyethylene withstands chemical reagents and is soluble in organic solvents only at elevated temperatures. This is a very good property of polyethylene but one which makes it difficult to measure molecular weight and solution properties. A few years ago, Nita Das and Palit reported that low density polyethylene was soluble near room temperature in binary mixtures of organic solvents such as xylene-carbondisulfide, cyclohexane-carbondisulfide, cyclohexane-trichloroethylene and cyclohexane-cyclohexanone systems.1 Their experiments were followed over a wide range of concentrations in our laboratory; we found that solutions of low density polyethylene in cyclohexane-carbondisulfide were converted to gels on cooling and the gels reverted to solutions when were warmed near room temperature. 2 · 3 Moreover, we found from X-ray diffraction patterns that the gels were crystalline. Our experimental results showed that gel-formation temperature depended on the molecular weight of the polymer as well as the concentration of the solution. Recently, Takahashi, Sakai, and Kato carried out similar experiments using three unfractionated branched polyethylenes and proposed a new theory for treating the gelmelting temperature of a branched polymer. 4 Their treatment is useful for estimating the size of a crystalline junction in the gel. In this study, gelation temperatures were measured for a series of fractionated low density polyethylene in cyclohexane-carbondisulfide and compared with the theory of Takahashi, Sakai, and Kato.

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